1. Field
The disclosed system and method pertain to detecting the coordinates of write points indicated at a panel and using those coordinates to affect an image displayed at a display screen, and pertain more particularly to resolving ambiguities when plural points are indicated concurrently that generate detected coordinates yielding combinations of coordinates that identify more potential write points than the actual write points.
2. Related Technology
In one known system, a user can designate points on an initial image shown at a display screen by touching a transparent touch panel over a display screen. The touch panel detects the coordinates of the points that the user touches and provides these coordinates to a computer that drives the display screen so that, for example, these points can be displayed superimposed on an initial image on the screen. Japanese Laid-Open Patent Application No. 8-305481 filed on Apr. 28, 1995 and laid open on Nov. 22, 1996, and incorporated herein by reference, discusses a coordinate input system of this type. The Japanese publication proposes the use of surface acoustic waves (SAW) to detect the coordinates of points that the user has indicated by touching a transparent writing panel, in the manner illustrated in FIG. 1. As seen in FIG. 1, the coordinate input device comprises a transparent writing panel 1 covering a display screen of an image display system. The transparent writing panel 1 is made of glass and is a rectangle having two vertical sides and two horizontal sides. Assuming that the X-axis is horizontal and the Y-axis is vertical, the position of a point on the writing panel 1 can be defined by a set of an X-coordinate and a Y-coordinate that are detected and are input to the image display system.
As seen in FIG. 1, a transmitting transducer 2 and a receiving transducer 3 are provided at the upper left and lower left corners, respectively, of the writing panel 1 and both face the right side of the writing panel 1. The transmitting transducer 2 transmits surface acoustic waves (SAW) horizontally to the right to propagate within the writing panel 1. The receiving transducer 3 receives the SAW from the transmitting transducer 2 through reflection. A transmitting transducer 4 and a receiving transducer 5 are provided at a lower left and right corners, respectively, of the writing panel 1 and both face the upper side of the writing panel 1. The transmitting transducer 4 transmits surface acoustic waves (SAW) vertically up so as to propagate the SAW within the writing panel 1. The receiving transducer 5 receives the SAW from the transmitting transducer 4 through reflection. Two arrays of reflectors 6 are provided on the horizontal sides of the writing panel 1, and two arrays of reflectors 7 are provided on the vertical sides of the writing panel 1, all arrayed at respective angles. Each of the reflectors 6 on the upper side of the writing panel 1 reflects a part of the SAW energy from the transmitting transducer 2 vertically down, and each of the reflectors 6 on the lower side of the writing board 1 further reflect the SAW energy received from the upper reflectors 6 to the receiving transducer 3. Each of the reflectors 7 on the left side of the writing panel 1 reflects the SAW energy from the transmitting transducer 4 horizontally to the right, and the reflectors 7 on the right side of the writing panel 1 further reflect the SAW energy received from the left-side reflectors 7 to the receiving transducer 5. Each reflector is partly transmissive so that it reflects a part of the SAW energy it receives and transmits a part of that SAW energy.
Still referring to FIG. 1, the tip of an input pen 8 is made of rubber or a rubber-like material. A user specifies a write point on the writing panel 1 by pressing or touching the tip of pen 8 at a specific position of the writing panel. SAW energy from the transmitting transducer 2 travels in the X-direction to the right. Each upper reflector 6 both transmits some of that SAW energy to the right in the X-direction and reflects some of the SAW energy down in the Y-direction to travel through the panel 1 and to be received by a corresponding one of the lower reflectors 6. The SAW from the transmitting transducer 4 similarly travel up along the left side of panel 1 to be partly transmitted and partly reflected at each of the left reflectors 7. The SAW energy that is reflected to the right in the X-direction by the left reflectors 7 travels within the writing panel 1 to the respective reflectors 7 at the right side of panel 1, and the SAW energy received at those reflectors 7 on the right side is sent to the receiving transducer 5 down in the Y-direction through the partly reflective and partly transmissive right reflectors 7. Whenever the tip of input pen 8 presses or touches the panel 1, the transmission of SAW energy through that point is inhibited or attenuated.
In the device of FIG. 1, the travel time of the SAW energy from the transmitting transducer 2 to the receiving transducer 3 via a respective pair of vertically aligned upper and lower reflectors 6 depends on the distances of those reflectors 6 from the left side of the writing panel 1 along the X-axis. By normalizing detection signals output by the receiving transducer 3, the distance of each of the reflectors 6 can be converted into a variable in terms of a time axis. The propagation of the SAW within the writing panel 1 is inhibited or attenuated only at the write point specified by the input pen 8. By locating a particular vertically aligned pair of reflectors 6 for which the detection signal output by receiving transducer 3 is inhibited or attenuated, the X-coordinate of the write point on the writing panel 1 can be detected. In a similar manner, by using the transmitting transducer 4, the receiving transducer 5 and reflectors 7, the Y-coordinate of the write point on the writing panel 1 can be detected.
Another type of known coordinate input device uses electromagnetic induction to detect the coordinates of an input image on a writing panel instead of using SAW energy.
Yet another earlier coordinate input device is discussed in Japanese Laid-Open Patent Application No.9-91094 filed on Sep. 21, 1995 and laid open on Apr. 4, 1997, and incorporated herein by reference. This Japanese application proposes the use of light to detect the coordinates of write points on a transparent writing panel. FIG. 2 illustrates a coordinate input device of this type. As seen in FIG. 2, this coordinate input device has a transparent writing panel 1 covering a display screen of an image display system, light scanners 21 and 22 at a lower left and right corners respectively, of the writing panel 1, a corner cube arrays 23 at the top of the writing panel 1, and corner cube arrays 24 and 25 at the left and right sides, respectively, of the writing panel 1. The transparent writing panel 1 is made of glass and is a rectangle having two vertical sides and two horizontal sides. Assuming that the X-axis is horizontal and the Y-axis is vertical, the position of a point that a user has designated on the writing panel 1 can be defined by a set of an X-coordinate and a Y-coordinate calculated from the angles at which the light is obscured and from the known geometry of the device.
In FIG. 2, each of the light scanners 21 and 22 rotates while sending out a beam of light and receiving a reflection of that beam. The corner cube arrays 23 to 25 reflect light from the light scanners 21 and 22 back toward the light scanners when a light beam is not obstructed. When a user presses or touches a specific position of the writing panel 1 (shown by the arrow in FIG. 2) with an implement that is in the path of the light beams from the light scanners 21 and 22 (and/of in the path of the reflected light beams), the light from (and/or to) the light scanners 21 and 22 is blocked or attenuated at the contact point so the respective light beams cannot reach the appropriate corner cube array(s) and/or be reflected back toward its source, or at least cannot do so in the same amplitude as when there is no obstruction. The light scanners 21 and 22 detect the angle of the respective light beams at the time there is no reflection (or there is only attenuated reflection) to thereby detect the angles labeled .alpha.1 and .beta.1 in FIG. 2. An arithmetic circuit calculates the coordinate pair (X1,Y1) from these two angles detected by the light scanners 21 and 22 and the known dimensions of the light panel 1.
One drawback of coordinate input devices using the propagation of SAW energy is that if two points are pressed or touched concurrently by implements such as the input pen 8, for example if the pen tip is kept on one point while another is touched, as illustrated in FIG. 3, the receiving transducer 3 detects two X-coordinates (x1 and x2) and the receiving transducer 5 also detects two Y-coordinates (y1 and y2) within a single time interval in which the coordinates are read, as illustrated in FIG. 4. In this case, the write point (X1,Y1) and (X2,Y2) are not identified unambiguously because the incorrect points (x1,y2) and (x2,y1) are also detected as a potential write point (shown by circles in FIG. 3).
In the device using rotating beams of light, if plural points are pressed by the user within a given time interval, as illustrated in FIG. 5 (shown by the arrow), two angles are detected by each of the light scanners 21 and 22 within a time interval in which the coordinates area read. The light scanners 21 detects the angles .alpha.2 and .alpha.3 and the light scanners 22 detects the angles .beta.2 and .beta.3. Again, the two correct points are (X1,Y1) and (X2,Y2) but the two incorrect points (shown by circles in FIG. 5) are also detected as potential write points.